Multiple Checkboxes using Flask WTForms

example.html

{% extends "layout_new.html" %}
{% block content_main %}
    <div class="content-section">
        <form method="POST" action="">
            {{ form.hidden_tag() }}
            <fieldset class="form-group">
                <legend class="border-bottom mb-4">User Choices</legend>
                {% if form.choices.errors %}
                <div class="invalid-feedback">
                    {% for error in form.choices.errors %}
                        <span>{{ error }}</span>
                    {% endfor %}
                </div>
                {% endif %}
                {% for choice in form.choices %}
                    <div class="form-check">
                        {{ choice(class="form-check-input") }}
                        {{ choice.label(class="form-check-label") }}
                    </div>
                {% endfor %}
            </fieldset>
            <div class="form-group">
                {{ form.submit(class="btn btn-outline-info") }}
            </div>
        </form>
    </div>
{% endblock content_main %}

form.py

class MultiCheckboxField(SelectMultipleField):
    widget = widgets.ListWidget(prefix_label=False)
    option_widget = widgets.CheckboxInput()

    
class ExampleForm(FlaskForm):
    choices = MultiCheckboxField('Routes', coerce=int)
    submit = SubmitField("Set User Choices")

route.py

@example.route("/example", methods=["GET", "POST"])
def example():
  form = ExampleForm()
  # populate the forms dynamically with the choices in the database
  form.check_options.choices = [(c.id, c.desc) for c in Choices.query.all()]
  # if it's a post request and we validated successfully
  if request.POST and form.validate_on_submit():
    # get our choices again, could technically cache these in a list if we wanted but w/e
    c_records = Choices.query.all()
    # need a list to hold our choices
    accepted = []
    # looping through the choices, we check the choice ID against what was passed in the form
    for choice in c_records:
      # when we find a match, we then append the Choice object to our list
      if choice.id in form.check_options.data:
        accepted.append(choice)
    # now all we have to do is update the users choices records
    user.choices = accepted
    db.session.add(user)
    db.session.commit(user)
  else:
    # tell the form what's already selected
    form.choices.data = [c.id for c in user.choices]
    return render_template('example.html', form=form)
  

user_modles.py

user_choices = app_db.Table('user_choices',
                   app_db.Column('user_id', app_db.Integer, app_db.ForeignKey('user.id'), primary_key=True),
                   app_db.Column('choice_id', app_db.Integer, app_db.ForeignKey('choice.id'), primary_key=True)
                   )

class User(db.Model, UserMixin):
  id = app_db.Column(app_db.Integer, primary_key=True)
  # other stuff as required
  choices = db.relationship('Choices', secondary=user_choices, lazy='subquery'
                            backref=db.backref('users_choice', lazy=True))

                            
class Choices(db.Model):
  id = app_db.Column(app_db.Integer, primary_key=True)
  desc = app_db.Column(app_db.String(25), nullable=False)

# tell the form what's already selected
form.choices.data = [c.id for c in user.choices]

Thanks! 👍

Very valuable. Thanks a lot!

How to set attributes (key and value) to each checkbox?